This invention is related to optical and acoustical imaging, including utilizing such images to perform optical data storage and retrieval, precision measurements on biological samples, wafers, integrated circuits, optical disks, and other samples, and to perform optical biopsies.
The invention relates to techniques for rapidly, accurately producing an in-focus image of an object, or a cross-section thereof, wherein the effect of light signals from out-of-focus foreground and/or background light sources are mostly eliminated with regard to both statistical and systematic errors. Confocal and confocal interference microscopy are finding many applications in, for example, the life sciences, the study of biological samples, industrial inspection, and semiconductor metrology. This is because of the unique three-dimensional imaging capability of these instruments.
Perhaps the most difficult multi-dimensional imaging is encountered when the background from out-of-focus images is significantly larger than the signal from the in-focus images. Such circumstances arise frequently in the study of thick samples, particularly when working in the reflection mode in contrast to the transmission mode of confocal systems.
There are two general approaches for determining the volume properties of three-dimensional microscopic specimens. Such approaches are based on conventional microscopy and confocal microscopy. Generally, the conventional microscopy approach requires less time to acquire the data but more time to process the data for a three-dimensional image, compared to the confocal microscopy approach.
In a conventional imaging system, when a part of the object to be imaged is axially displaced from its best focus location, the image contrast decreases but the brightness remains constant so that displaced, unfocused parts of the image interfere with the view of focused parts of object.
If the system""s point-spread function is known and images are obtained for each independent section of the object, known computer algorithms can be applied to such images to effectively remove the signal contributed by the out-of-focus light and produce images that contain only in-focus data. Such algorithms are of several distinct types, are referred to as xe2x80x9ccomputer deconvolutions,xe2x80x9d and generally require expensive computer equipment and considerable computing time and considerable amounts of data to obtain the desired statistical accuracy.
The wide field method (WFM) (D. A. Agard and J. W. Sedat, xe2x80x9cThree-Dimensional Analysis of Biological Specimens Utilizing Image Processing Techniques,xe2x80x9d Proc. Soc. PhotoOpt. Instrum. Eng., SPIE, 264, 110-117, 1980; D. A. Agard, R. A. Steinberg, and R. M. Stroud, xe2x80x9cQuantitative Analysis of Electrophoretograms: A Mathematical Approach to Super-Resolution,xe2x80x9d Anal. Biochem. 111, 257-268, 1981; D. A. Agard, Y. Hiraoka, P. Shaw, and J. W. Sedat, xe2x80x9cFluorescence Microscopy in Three Dimensions,xe2x80x9d Methods Cell Biol. 30, 353-377, 1989; D. A. Agard, xe2x80x9cOptical Sectioning Microscopy: Cellular Architecture in Three Dimensions,xe2x80x9d Annu. Rev. Biophys. Bioeng. 13, 191-219, 1984; Y. Hiraoka, J. W. Sedat, and D. A. Agard, xe2x80x9cThe Use of a Charge-Coupled Device for Quantitative Optical Microscopy of Biological Structures,xe2x80x9d Sci. 238, 36-41, 1987; W. Denk, J. H. Strickler, and W. W. Webb, xe2x80x9cTwo-Photon Laser Scanning Fluorescence Microscopy,xe2x80x9d Sci. 248, 73-76, 1990) uses a conventional microscope to sequentially acquire a set of images of adjacent focus planes throughout the volume of interest. Each image is recorded using a cooled charge-coupled device (CCD) image sensor (J. Kristian and M. Blouke, xe2x80x9cCharge-coupled Devices in Astronomy,xe2x80x9d Sci. Am. 247, 67-74, 1982) and contains data from both in-focus and out-of-focus image planes.
The technique of laser computed tomography is implemented using a conventional microscope. The system discussed by S. Kawata, O. Nakamura, T. Noda, H. Ooki, K Ogino, Y. Kuroiwa, and S. Minami, xe2x80x9cLaser Computed-Tomography Microscope,xe2x80x9d Appl. Opt. 29, 3805-3809 (1990) is based on a principal that is closely related to the technique of X-ray computed tomography, but uses three-dimensional volume reconstruction rather than two-dimensional slice reconstruction. Projected images of a thick three-dimensional sample are collected with a conventional transmission microscope modified with oblique illumination optics, and the three-dimensional structure of the interior of the sample is reconstructed by a computer. Here, the data is acquired in a time short compared to that required to process data for a three-dimensional image. In one experiment by Kawata et al., ibid., the 80xc3x9780xc3x9736-voxel reconstruction required several minutes to collect all projections and send them to a minicomputer. Approximately thirty minutes then were required for digital reconstruction of the image, in spite of utilizing a vector processor at a speed of 20 million floating point operations per second (MFLOPS).
In a conventional point or pinhole-confocal microscope, light from a point source is focused within a very small space, known as a spot. The microscope focuses light reflected from, scattered by, or transmitted through the spot onto a point detector. In a reflecting point-confocal microscope the incident light is reflected or back-scattered by that portion of the sample in the spot. Any light which is reflected or back-scattered by the sample outside of the spot is not well focused onto the detector, thus it is spread out so the point detector receives only a small portion of such reflected or back-scattered light. In a transmitting point-confocal microscope, incident light is transmitted unless it is scattered or absorbed by that portion of the sample in the spot. Generally, the point source and point detector are approximated by placing masks containing a pinhole in front of a conventional light source and a conventional detector, respectively.
Similarly, in a conventional slit-confocal microscope system, light from a line source is focused into a very narrow elongated space, which is also known as a spot. The slit-confocal microscope focuses light reflected from, scattered by or transmitted through the spot onto a line detector. The line source and line detector can be approximated using a mask with a slit in front of a conventional light source and row of conventional detectors, respectively. Alternately, a line source can be approximated by sweeping a focused laser beam across the object to be imaged or inspected.
Since only a small portion of the object is imaged by the confocal microscope, either the object to be imaged must be moved, or the source and detector must be moved, in order to obtain sufficient image data to produce a complete two-dimensional or three-dimensional view of the object. Previous slit-confocal systems have moved the object linearly in a direction perpendicular to the slit to obtain successive lines of two-dimensional image data. On the other hand, point-confocal systems having only one pinhole have to be moved in a two-dimensional manner in order to acquire two-dimensional image data and in a three-dimensional manner in order to acquire a three-dimensional set of image data. The raw image data are typically stored and later processed to form a two-dimensional cross-section or a three-dimensional image of the object that was inspected or imaged. The reduced sensitivity to out-of-focus images relative to conventional microscopy leads to improved statistical accuracy for a given amount of data and the processing operation is considerably simpler in comparison to that required when processing data obtained in conventional microscopy approach.
In a system known as the Tandem Scanning Optical Microscope (TSOM), a spiral pattern of illumination and detector pinholes are etched into a Nipkow disk so, as the disk rotates, the entire stationary object is scanned in two dimensions [cf. M. Pxc3xa9tran and M. Hadravsky, xe2x80x9cTandem-Scanning Reflected-Light Microscope,xe2x80x9d J. Opt. Soc. A. 58(5), 661-664 (1968); G. Q. Xiao, T. R. Corle, and G. S. Kino, xe2x80x9cReal-Time Confocal Scanning Optical Microscope,xe2x80x9d Appl. Phys. Lett. 53, 716-718 (1988)]. In terms of the optical processing, the TSOM is basically a single point confocal microscope with a means for efficiently scanning a two-dimensional section one point at a time.
Examples of two techniques implemented to reduce the amount of scanning required to obtain a two-dimensional image with a confocal arrangement are found in the work of H. J. Tiziani and H.-M. Uhde, xe2x80x9cThree-Dimensional Analysis by a Microlens-Array Confocal Arrangement,xe2x80x9d Appl. Opt. 33(4), 567-572 (1994) and in the patent of P. J. Kerstens, J. R. Mandeville, and F. Y. Wu, xe2x80x9cTandem Linear Scanning Confocal Imaging System with Focal Volumes at Different Heights,xe2x80x9d (U.S. Pat. No. 5,248,876 issued September 1993). The microlens-array confocal arrangement of Tiziani and Uhde ibid. has out-of-focus image discrimination that is the same as using a multi-pinhole source and multi-element detector in a confocal configuration. Such a system allows for a number of points to be examined simultaneously but at a compromise in discrimination against out-of-focus images. The higher the density of microlenses, the poorer the ability of the system to discriminate against out-of-focus images, and consequently, an increase in complexity and cost of the computer deconvolutions required to produce a three-dimensional image. Further, the Tiziani and Uhde ibid. system has serious limitations in axial range. This range cannot exceed the focal length of the microlens, which is proportional to the diameter of the microlens for a given numerical aperture. Therefore, as the density of the microlenses is increased, there is an associated decrease in the permitted axial range.
The Kerstens et al., ibid. system incorporates a number of pinholes and matching pinpoint detectors in a confocal arrangement to allow for a number of points to be examined simultaneously. However, as noted in the preceding paragraph, this gain is at a compromise in discrimination against out-of-focus images and as a result an increase in complexity and cost of required subsequent computer deconvolutions. The higher the density of pinholes, the poorer the ability of the system to discriminate against out-of-focus images. The highest discrimination would be achieved when using only one pinhole.
Application of confocal microscopes to inspection of electronics was suggested in T. Zapf and R. W. Wijnaendts-van-Resandt, xe2x80x9cConfocal Laser Microscope For Submicron Structure Measurement,xe2x80x9d Microelectronic Engineering 5, 573-580 (1986) and J. T. Lindow, S. D. Bennett, and I. R. Smith, xe2x80x9cScanned Laser Imaging for Integrated Circuit Metrology,xe2x80x9d SPIE, 565, 81-87 (1985). The axial discrimination provided by confocal systems make them useful in the semi-conductor manufacturing environment. For example, such systems could provide for improved inspection of height dependent features such as delamination, blisters, and thickness of structures and coatings. However, there are some problems associated with using confocal imaging systems for inspection of electronics. For example, single pinhole systems require too much time for scanning the object in two directions. Optical systems for scanning a laser beam over the object are too complex; and the spinning disk approach used in the previous TSOM resulted in alignment and maintenance problems.
The number of different depth slices required (and therefore the amount of image data collected) depends upon the range of height that must be measured, and also upon the desired height resolution and performance of the optical system. For typical electronics inspection, images of 10 to 100 different depth slices would be required. Furthermore, data in several color bands may be required to differentiate materials. In confocal imaging systems, a separate two-dimensional scan is required for each desired elevation. If data for multiple color bands is desired, then multiple two-dimensional scans at each elevation are required. By shifting the focus level, similar data can be obtained from adjacent planes and a three-dimensional intensity data set can be acquired.
Thus, none of the prior art confocal microscopy systems can be configured for rapid and/or reliable three-dimensional tomographic imaging, especially in the field of inspection or imaging.
Although the confocal approach is more straightforward and works better, for example in confocal fluorescence work, when the concentration of stained structure is high, the conventional microscopy approach still has several practical advantages. The most important of these is that the latter can utilize dyes that are excited in the ultraviolet (UV) range and these often seem more robust and efficient than those excited in the visible range. Although, a UV laser can be incorporated as the light source of a confocal microscope [M. Montag, J. Kululies, R. Jxc3x6rgens, H. Gundlach, M. F. Trendelenburg, and H. Spring, xe2x80x9cWorking with the Confocal Scanning UV-Laser Microscope: Specific DNA Localization at High Sensitivity and Multiple-Parameter Fluorescence, xe2x80x9d J. Microsc(Oxford) 163 (Pt. 2), 201-210, 1991; K. Kuba, S.-Y. Hua, and M. Nohmi, xe2x80x9cSpatial and Dynamic Changes in Intracellular Ca2+ Measured by Confocal Laser-Scanning Microscopy in Bullfrog Sympatetic Ganglion Cells,xe2x80x9d Neurosci. Res. 10, 245-259, 1991; C. Bliton, J. Lechleiter and D. E. Clapham, xe2x80x9cOptical Modifications Enabling Simultaneous Confocal Imaging With Dyes Excited by Ultraviolet- and Visible-Wavelength Light,xe2x80x9d J. Microsc. 169(Pt. 1), 15-26, 1993], or UV dyes can be excited with infrared (IR) light using the xe2x80x9ctwo photonxe2x80x9d technique (W. Denk, et al., ibid.), these techniques involve considerable expense and practical difficulty.
Furthermore, the cooled CCD detectors used in conventional microscopy systems collect the data in parallel rather than serially, as does the photomultiplier (PMT) in a confocal microscopy system. As a result, if the CCD can be made to read out more rapidly without degrading its performance, the three-dimensional data recording rate of the conventional microscopy system may prove to be significantly higher than that of the confocal microscopy system, even though the time needed for computer deconvolution computations means that there might be an additional delay before the data could be actually viewed as three-dimensional image.
The signal-to-noise ratio in relation to statistical accuracy must also be considered when making a choice between a CCD detector used to record in parallel a two-dimensional data array and a slit or pinhole confocal microscope. The well capacity of a two-dimensional CCD pixel is of the order of 200,000 electrons. This limits the statistical accuracy that can be achieved in a single exposure as compared to that achievable with other photoemissive detectors such as PMT""s or photovoltaic devices. Consequently, for those applications where the out-of-focus background contributions are significantly larger than the in-focus image signals, consideration of the signal-to-noise ratio may lead to the conclusion that a one-dimensional parallel recording of data in a slit confocal microscope will perform better than a two-dimensional recording of data in a standard microscope configuration or a point by point recording of data in a single pinhole confocal microscope will perform better than a one-dimensional parallel recording of data in a slit confocal microscope, all other considerations being equal.
When the consideration of statistical accuracy as measured by the signal-to-noise ratio influences the selection of a system such as a slit confocal microscope over a standard microscope, or a single pinhole confocal microscope over a slit confocal microscope, the residual signals from the out-of-focus images for the system chosen can be comparable to or larger than the in-focus signals. Such is the case for example when examining deep into biological samples at optical wavelengths where scattering of optical radiation dominates over absorption. In this case, one is left with the need for a lengthy computer deconvolution, i.e. long compared to the time required to acquire the data. Note that this is in general true for the single pinhole confocal microscope as well as the slit confocal microscope when looking for an in-focus image signal that is much smaller than the residual out-of-focus image signals.
Although it is easier to accurately digitize the signal from a CCD detector than from a PMT (J. B. Pawley, xe2x80x9cFundamental and Practical Limits in Confocal Light Microscopy,xe2x80x9d Scanning 13, 184-198, 1991), the PMT is a single device that can be accurately characterized, whereas the CCD is actually a large array of discrete detectors and additional noise is associated with correcting for the pixel-to-pixel variations in sensitivity and offset that characterize its operation (Y. Hiraoka, et al., ibid.; J. E. Wampler and K. Kutz, xe2x80x9cQuantitative Fluorescence Microscopy Using Photomultiplier Tubes and Imaging Detectors,xe2x80x9d Methods Cell Biol. 29, 239-267, 1989; Z. Jericevic, B. Wiese, J. Bryan, and L. C. Smith, xe2x80x9cValidation of an Imaging System: Steps to Evaluate and Validate a Microscope Imaging System for Quantitative Studies,xe2x80x9d Methods Cell Biol. 30, 47-83, 1989).
It should be noted that the above distinction between the photodetectors used in the two methods of three-dimensional microscopy should not be considered to be complete, because the cooled CCD detector is the most suitable photodetector for those confocal microscopes that accomplish the scanning function by using holes in a spinning disk (Petran, et al., ibid.; Xiao, et al., ibid.).
Another technique known as xe2x80x9coptical coherence-domain reflectometryxe2x80x9d (OCDR) has been used to obtain information about the three-dimensional properties of a system. This method is described in the following articles: (1) xe2x80x9cOptical Coherence-Domain Reflectometry: A New Optical Evaluation Technique,xe2x80x9d by R. C. Youngquist, S. Carr, and D. E. N. Davies, Opt. Lett. 12(3), 158-160 (1987); (2) xe2x80x9cNew Measurement System for Fault Location in Optical Waveguide Devices Based on an Interferometric Technique,xe2x80x9d K. Takada, I. Yokohama, K. Chida, and J. Noda, Appl. Opt. 26(9), pp. 1603-1606 (1987); (3) xe2x80x9cGuided-Wave Reflectometry with Micrometer Resolution,xe2x80x9d B. L. Danielson and C. D. Whittenberg, Appl. Opt. 26(14), 2836-2842 (1987). The OCDR method differs from the coherent optical time domain reflectometry (OTDR) technique in that instead of a pulsed light source one uses a broadband continuous-wave source with a short coherence length. The source beam enters an interferometer in which one arm has a movable mirror, with the reflected light from this mirror providing a reference beam, and the other arm contains the optical system being tested. The interference signal in the coherently mixed reflected light from the two arms is detected by the usual heterodyne method and yields the desired information about the optical system.
The heterodyne detection of the backscattered signals in the OCDR technique is accomplished by the method of xe2x80x9cwhite-light interferometry,xe2x80x9d in which the beam is split into the two arms of an interferometer, reflected by the adjustable mirror and the backscattering site, and coherently recombined. This method utilizes the fact that interference fringes will appear in the recombined beam only when the difference in the optical path length between the two arms is less than the coherence length of the beam. The OCDR systems described in references (1) and (3) above make use of this principle, and reference (3) shows interferograms of fiber gaps in test systems obtained by scanning the adjustable mirror and measuring the strength of the recombined signal. Reference (1) also describes a modified method in which the mirror in the reference arm oscillates at a controlled frequency and amplitude, causing a Doppler shift in the reference signal, and the recombined signal is fed into a filtering circuit to detect the beat frequency signal.
Another variation of this technique is illustrated in reference (2), in which the reference arm mirror is at a fixed position and the difference in optical path lengths in the two arms may exceed the coherence length. The combined signal is then introduced into a second Michelson interferometer with two mirrors, one fixed in position and the other being moveable. This moveable mirror is scanned and the difference in path length between the arms of the second interferometer compensates for the delay between the backscattered and reference signals at discrete positions of the moveable mirror corresponding to the scattering sites. In practice, an oscillating phase variation at a definite frequency is imposed on the signal from the backscattering site by means of a piezoelectric transducer modulator in the fiber leading to this site. The output signal from the second Michelson interferometer is fed to a lock-in amplifier, which detects the beat frequency signal arising from both the piezoelectric transducer modulation and the Doppler shift caused by the motion of the scanning mirror. This technique has been used to measure irregularities in glass waveguides with a resolution as short as 15 xcexcm [xe2x80x9cCharacterization of Silica-Based Waveguides with a Interferometric Optical Time-Domain Reflectometry System Using a 1.3-xcexcm-Wavelength Superluminescent Diode,xe2x80x9d K. Takada, N. Takato, J. Noda, and Y. Noguchi, Opt. Lett. 14(13), 706-708 (1989)].
Another variation of the OCDR is the dual-beam partial coherence interferometer (PCI) which has been used to measure the thickness of fundus layers in the eye [xe2x80x9cMeasurement of the Thickness of Fundus Layers by Partial Coherence Tomography,xe2x80x9d by W. Drexler, C. K. Hitzenberger, H. Sattmann, and A. F. Fercher, Opt. Eng. 34(3), 701-710 (1995)]. In the PCI used by Drexler, et al., an external Michelson interferometer splits a light beam of high spatial coherence but very short coherence length of 15 xcexcm into two parts: the reference beam (1) and the measurement beam (2). At the interferometer exit, these two components are combined again to form a coaxial dual beam. The two beam components, which have a path difference of twice the interferometer arm length difference, illuminate the eye and are reflected at several intraocular interfaces, which separate media of different refractive index. Therefore each beam component (1 and 2) is further split into subcomponents by reflection at these interfaces. The reflected subcomponents are superimposed on a photodetector. If the optical distance between two boundaries within the eye equals twice the interferometer arm length difference, there are two subcomponents that will travel over the same total path length and will consequently interfere. Each value of the interferometer arm length difference where an interference pattern is observed, is equal to an intraocular optical distance. Provided that there is no other strong reflection nearby, the absolute position of these interfaces can be determined in vivo with a precision of 5 xcexcm. However, the PCI suffers from limitations due to motion of the object during the time required for the 3-D scanning.
Another variation of the OCDR called optical coherent tomography (OCT) has been reported for in vivo retinal imaging by E. A. Swanson, J. A. Izatt, M. R. Hee, D. Huang, C. P. Lin, J. S. Schuman, C. A. Puliafito, and J. G. Fujimoto, xe2x80x9cIn Vivo Retinal Imaging by Optical Coherence Tomography,xe2x80x9d Opt. Lett. 18(21), 1864-1866 (1993), and E. A. Swanson, D. Huang, J. G. Fujimoto, C. A Puliafito, C. P. Lin, and J. S. Schuman, xe2x80x9cMethod and Apparatus for Optical Imaging with Means for Controlling the Longitudinal Range of the Sample,xe2x80x9d U.S. Pat. No. 5,321,501, issued Jun. 14, 1994. The above referenced patent describes a method and apparatus for performing optical imaging on a sample wherein longitudinal scanning or positioning in the sample is provided by either varying relative optical path lengths for an optical path leading to the sample and to a reference reflector, or by varying an optical characteristic of the output from an optical source applied to the apparatus. Transverse scanning in one or two-dimensions is provided on the sample by providing controlled relative movement between the sample and a probe module in such direction and/or by steering optical radiation in the probe module to a selected transverse position. The reported spatial resolution is  less than 20 xcexcm with a high sensitive (100 dB dynamic range). However the OTC suffers from limitations due to motion of the object during the time required for the three-dimensional scanning.
Optical interferometric profilers are widely used for three-dimensional profiling of surfaces when noncontact methods are required. These profilers typically use phase-shifting interferometric (PSI) techniques and are fast, accurate, and repeatable, but suffer from the requirement that the surface be smooth relative to the mean wavelength of the light source. Surface discontinuities greater than a quarter-wavelength (typically 150 nm) cannot be unambiguously resolved with a single-wavelength measurement because of the cyclic nature of the interference. Multiwavelength measurements can extend this range, but the constraints imposed on wavelength accuracy and environmental stability can be severe (U.S. Pat. No. 4,340,306 issued Jul. 20, 1982 to N. Balasubramanian entitled xe2x80x9cOptical System for Surface Topography Measurement.xe2x80x9d)
Profilers based on scanning white-light interferometry (SWLI) overcome many of the limitations of conventional PSI profilers for the measurement of rough or discontinuous surfaces. A number of articles describe this technique in detail [cf. Refs. 2-7 in L. Deck and P. de Groot, Appl. Opt. 33(31), 7334-7338 (1994)]. Typically these profilers record the position of a contrast reference feature (i.e., peak contrast or peak fit) for each point in the field of view while axially translating one arm of an equal-path interferometer illuminated with a broadband source. A common problem with this technique is the enormous amount of computation required for calculating the contrast for each point in real time. Often the contrast calculation alone is insufficiently precise because of the discrete sampling interval, forcing either an increase in the sampling density or incorporating an interpolation technique, both of which further slow the acquisition process. The Coherence Probe Microscope (CPM) is an example of this class of profiler [U.S. Pat. No. 4,818,110 issued Apr. 4, 1989 to M. Davidson entitled xe2x80x9cMethod and Apparatus of Using a Two Beam Interference Microscope for Inspection of Integrated Circuits and the Likexe2x80x9d; M. Davidson, K. Kaufman, I. Mazor, and F. Cohen, xe2x80x9cAn Application of Interference Microscope to Integrated Circuit Inspection and Metrology,xe2x80x9d SPIE, 775, 233-247 (1987); U.S. Pat. No. 5,112,129 issued May 12, 1992 to M. Davidson, K. Kaufman, and I. Mazor entitled xe2x80x9cMethod of Image Enhancement for the Coherence Probe Microscope with Applications to Integrated Circuit Metrology.xe2x80x9d]. Profilers in general and the CPM in particular are not able to work with three-dimensional objects, have the background typical of a conventional interference microscopy, are sensitive to vibrations, and require computer intensive analysis.
Profilers based on triangulation also overcome many of the limitations of conventional PSI profilers but suffer from reduced height and lateral space resolution and have a large background form out-of-images. An application of this technique is found in the paper entitled xe2x80x9cParallel Three-Dimensional Sensing by Color-Coded Triangulationxe2x80x9d by G. Hausler and D. Ritter, Appl. Opt., 32(35), 7164-7169 (1993). The method used by Hxc3xa4usler and Ritter, ibid., is based on the following principle: a color spectrum of a white-light source is imaged onto the object by illumination from one certain direction. The object is observed by a color TV camera from a direction of observation which is different from the direction of illumination. The color (hue) of each pixel is a measure of its distance from a reference plane. The distance can be evaluated by the three(red-green-blue) output channels of a charge coupled device (CCD) camera and this evaluation can be implemented within TV real time. However, the resolution in height and in one lateral spatial dimension is considerably reduced below that achieved with PSI and SWLI, there is a large background, and the triangulation profiler has the noise characteristics of non-interferometric measurement techniques. In addition, the triangulation profiler is limited to surface profiling.
One of the problems encountered in white-light interferometry (WLI) is the problem of phase ambiguities. A profilometry method that has been received attention with respect to the phase ambiguity problem is the dispersive interferometric profilometer (DIP) proposed by J. Schwider and L. Zhou in a paper entitled xe2x80x9cDispersive Interferometric Profilometer,xe2x80x9d Opt. Lett. 19(13), 995-997 (1994). A similar approach for WLI has also been reported by U. Schnell, E. Zimmermann, and R. Dandliker in an article entitled xe2x80x9cAbsolute Distance Measurement With Synchronously Sampled White-Light Channelled Spectrum Interferometry,xe2x80x9d Pure Appl. Opt. 4, 643-651 (1995).
In general, the phase ambiguity problem can be completely avoided with the use of DIP. In the DIP apparatus, a parallel beam of a white-light source perpendicularly impinges upon the real wedge of a Fizeau interferometer in front of an apochromatic microscope objective. The Fizeau interferometer is formed by the inner surface of the reference plate and the object surface. Then the light is reflected back onto the slit of a grating spectrometer, which disperses the so far invisible fringe pattern and projects the spectrum onto a linear array detector. On the detector each point of the surface selected by the slit of the spectrometer furnishes a dispersed spectrum of the air gap in the Fizeau interferometer. The fringe patterns can be evaluated by use of Fourier-transform and filtering methods to obtain the phase information from the intensity distribution of a wedge-type interferogram.
Although the phase ambiguity problem can be avoided with the use of DIP, DIP is not suitable in applications requiring the examination of three-dimensional objects. This is a consequence of the intrinsic relatively large background produced in DIP from out-of-focus images. The background problem is comparable to the background problem faced when trying to produce three-dimensional images using standard interference microscopy.
An apparatus and method for making spectrally-resolved measurements of light reflected, emitted or scattered from a specimen was disclosed by A. E. Dixon, S. Damaskinos, and J. W. Bowron in U.S. Pat. No. 5,192,980 issued Mar. 9, 1993 and entitled xe2x80x9cApparatus and Method for Spatially- and Spectrally-Resolved Measurementsxe2x80x9d. In one set of embodiments of the apparatus and method of Dixon et al., properties of a specimen are characterized in terms of the intensity of light reflected, emitted or scattered from the specimen wherein the apparatus and method are comprised of non interferometric, non confocal type with a dispersive element preceding the detector. This set of embodiments of Dixon et al. have a large background from out-of-focus images intrinsic to the standard microscope, the set of embodiments being of the non confocal type.
The apparatus and method of Dixon et al. also includes a non interferometric confocal embodiment which permits measurements with reduced background. However the limitation to making intensity measurements for the confocal embodiment as well as for the non confocal embodiments, a consequence of using a non interferometric technique, poses serious limitations on the information about the specimen that can be acquired from reflected or scattered light. Intensity measurements yield information about the square of the magnitude of an amplitude of light reflected or scattered by the specimen with the consequence that information about the phase of the amplitude of reflected or scattered light is lost. The apparatus and method of Dixon et al. further includes an embodiment which incorporates a Fourier Transform spectrometer in a non confocal imaging system. The Fourier Transform spectrometer embodiment of Dixon et al. has the disadvantage of a large background from out-of-focus images intrinsic to nonconfocal imaging systems.
Apparatus for making simultaneous multiple wavelength measurements with a non-interferometric, confocal imaging system has been disclosed by G. Xiao in U.S. Pat. No. 5,537,247 issued July 1996 and entitled xe2x80x9cSingle Aperture Confocal Imaging Systemxe2x80x9d. The apparatus of Xiao is comprised of a confocal scanning imaging system which utilizes only one aperture for both the incident light from the light source and return light from the object and a series of beam splitters and optical wavelength filters to selectively direct return light of differing wavelengths to a series of detectors, respectively. The Xiao apparatus has an advantage of making simultaneous measurements at different wavelengths and the merits of a confocal imaging system with respect to reduced background from out-of-focus images. However the limitation to making intensity measurements, a consequence of using a non interferometric technique, poses serious limitations on the information about the specimen that can be acquired from reflected or scattered light. Intensity measurements yield information about the square of the magnitude of an amplitude of light reflected or scattered by the specimen with the consequence that information about the phase of the amplitude of reflected or scattered light is lost.
It was pointed out in a paper by G. Q. Xiao, T. R. Corle, and G. S. Kino entitled xe2x80x9cReal-time Confocal Scanning Optical Microscope,xe2x80x9d Appl. Phys. Lett., 53(8), 716-718 (1988) that when using white light in a confocal microscope, the chromatic aberrations of the objective lens ensures that images from different heights in the specimen are all present and all in focus but at different colors. Xiao et al. demonstrated this by producing images of a silicon integrated circuit at four different wavelengths. H. J. Tiziani and H.-M. Uhde described in a paper entitled xe2x80x9cThree-Dimensional Image Sensing by Chromatic Confocal Microscopy,xe2x80x9d Appl. Opt., 33(10), 1838-1843 (1994) a white light, non interferometric, confocal microscope in which chromatic aberration was deliberately introduced into the microscope objective for the purpose of obtaining height information without physically scanning the object. A camera with black-and-white film sequentially combines, with three selected chromatic filters, intensity and tone of color of each object point. Although confocal microscopes are used in both of the works described by Xiao et al. and Tiziani and Uhde and therefore have reduced background from out-of-focus images, they are limited to making intensity measurements. The limitation to making intensity measurements, a direct consequence of using a non interferometric technique, poses serious limitations on the information about the specimen that can be acquired from reflected or scattered light as noted in reference to the patents by Dixon et al. and Xiao.
An interference microscope has been described in papers by G. S. Kino and S. C. Chim, xe2x80x9cMirau Correlation Microscope,xe2x80x9d Appl. Opt., 26(26), 3775-3783 (1990) and S. S. C. Chim and G. S. Kino, xe2x80x9cThree-Dimensional Image Realization in Interference Microscopy,xe2x80x9d Appl. Opt., 31(14), 2550-2553 (1992) which is based on a Mirau interferometer configuration. The apparatus of Kino and Chim employs an interferometric, non confocal microscope with a spatially and temporally incoherent light source and uses as the detected output the correlation signal between the beams reflected from the object and from a mirror, respectively. It is possible with the apparatus of Kino and Chim to measure both amplitude and phase of the beam reflected from the object. However, the interferometric apparatus of Kino and Chim has the disadvantage of a serious background problem, the level of background from out-of-focus images being typical of that found in a standard interference, nonconfocal microscopy system.
An interferometric apparatus has been disclosed by A. Knxc3xcttel in U.S. Pat. No. 5,565,986 issued Oct. 15, 1996 and entitled xe2x80x9cStationary Optical Spectroscopic Imaging in Turbid Objects by Special Light Focusing and Signal Detection of Light with Various Optical Wavelengthsxe2x80x9d to obtain a spectroscopic image of an object, displaying both spatial resolution in a lateral direction and a field of view in a depth direction. The apparatus described by Knuttel has a nonconfocal imaging system and typically includes a dispersive optical element in an arm of an interferometer and a chromatic object lens. The dispersive element makes it possible to record information about the scattered light amplitude at different optical wavelengths, the use of an interferometer makes it possible to record information about the magnitude and phase of the amplitude of reflected or scattered light, and the use of a chromatic object lens makes it possible to record information about a field of view in a depth direction. However, the interferometric apparatus of Knxc3xcttel has a serious background problem, the level of the background being typical of that found in a standard interference, nonconfocal microscopy system.
One of the primary objectives of an embodiment of the apparatus of Knxc3xcttel was to be able to image simultaneously two regions of an object separated in a depth dimension by using two different orders of a chromatic object lens comprised in part of a zone plate. As a consequence, the signals recorded by the detector of this embodiment are comprised of superimposed images from the two separated depth positions in the object. Therefore, in addition to the presence of a high background from out-of-focus images as previously noted, a complex inversion calculation must be performed by the computer to extract the image for a given depth from the superimposed in focus images. There is a serious problem encountered with the type of inversion calculation required for superimposed images as acquired with the referenced embodiment of Knxc3xcttel: the results of the inversion calculations are relatively accurate near the surface of the object but rapidly degrade as the depth in the sample increases. This problem is generally not encountered in inversion calculations where there is only one point of the object in-focus at the detector.
The above cited background problem encountered in interference microscopy is reduced in an interference version of the confocal microscope described by D. K. Hamilton and C. J. R. Sheppard in an article entitled xe2x80x9cA Confocal Interference Microscopexe2x80x9d, Optica Acta, 29(12), 1573-1577 (1982). The system is based on the confocal microscope in which the object is scanned relative to a focused laser spot, the laser spot being arranged to coincide with the back-projected image of a point detector. An interference form of the reflection confocal microscope is based on a Michelson interferometer in which one beam is focused onto the object. This system has the important property of a reduced background from out-of-focus images intrinsic to confocal microscopy systems. However, the confocal interference microscope of Hamilton and Sheppard, ibid., measures the reflected signal at only one point at a time in a three-dimensional object. The scanning of the object one point at a time also makes the system sensitive to sample motion unrelated to the scan during the required data acquisition.
A major component that is important in the effective utilization of high-performance computers is memory. Because of the huge data storage requirements of these instruments, compact, low-cost, very high-capacity, high-speed memory devices are needed to handle the high data volume afforded by parallel computing. Such data storage requirements may be provided by a three-dimensional memory.
In a two-dimensional memory, the maximum theoretical storage density (proportional to 1/xcex2) is of the order of 3.5xc3x97108 bits/cm2 for xcex=532 nm, whereas in a three-dimensional memory the maximum storage density is of the order of 6.5xc3x971012 bits/cm3. These maximum values represent upper limits to the storage capacity when using a single bit binary format at each memory site. These upper limits can be increased by using a recording medium where different levels of amplitude or amplitude and phase information are recorded. Holographic recording in phase-recording media is an example of the latter mode.
In the different modes of recording, the mode of single bit binary format, amplitude in base N format or amplitude and phase in (base N)xc3x97(base M) format, at each memory site, the size of a voxel at a memory site that can be used, and therefore storage density, is limited by the signal-to-noise ratio that can be obtained, the signal-to-noise ratio generally being inversely proportional to the volume of the voxel. In particular, for the amplitude or amplitude and phase recording modes, the number of independent pieces of information that can be stored in a voxel is also limited by the signal-to-noise ratio that can be obtained.
What is needed is a system that combines a sensitivity of image data to out-of-focus images that is reduced below that inherent in prior art confocal and confocal interference microscopy, the reduced sensitivity of the image data to out-of-focus images being with respect to both systematic and statistical errors; a reduced requirement of computer deconvolutions associated with reduced sensitivity to out-of-focus images; the potential for high signal-to-noise ratios intrinsic to confocal interference microscopy systems; capacity to record in parallel the data for an axial or transverse direction; and the potential to measure the complex amplitude of the scattered and/or the reflected light beam.
Accordingly, it is an object of the invention to furnish method and apparatus for reading information from locations at different depths within an optical disk.
It is an object of the invention to furnish method and apparatus for reading information from locations at multiple depths within an optical disk.
It is an object of the invention to furnish method and apparatus for reading information simultaneously from locations at multiple depths within an optical disk.
It is an object of the invention to furnish method and apparatus for reading information from locations at multiple tracks on or within an optical disk.
It is an object of the invention to furnish method and apparatus for reading information simultaneously from locations at multiple tracks on or within an optical disk.
It is an object of the invention to furnish method and apparatus for reading information simultaneously from locations at multiple tracks and multiple locations on the tracks on or within an optical disk.
It is an object of the invention to furnish method and apparatus for reading information simultaneously from locations at multiple depths and multiple tracks within an optical disk.
It is an object of the invention to furnish method and apparatus for writing information to locations at multiple depths within an optical disk.
It is an object of the invention to furnish method and apparatus for writing information simultaneously to locations at multiple depths within an optical disk.
It is an object of the invention to furnish method and apparatus for writing information to locations at multiple tracks on or within an optical disk.
It is an object of the invention to furnish method and apparatus for writing information simultaneously to locations at multiple tracks on or within an optical disk.
It is an object of the invention to furnish method and apparatus for writing information simultaneously to locations at multiple depths and multiple tracks within an optical disk.
It is an object of the invention to furnish method and apparatus for writing information to locations at multiple depths within an optical disk with a higher density.
It is an object of the invention to furnish method and apparatus for writing information simultaneously to locations at multiple depths within an optical disk with a higher density.
It is an object of the invention to furnish method and apparatus for writing information to locations at multiple tracks on or within an optical disk with a higher density.
It is an object of the invention to furnish method and apparatus for writing information simultaneously to locations at multiple tracks on or within an optical disk with a higher density.
It is an object of the invention to furnish method and apparatus for writing information simultaneously to locations at multiple depths and multiple tracks within an optical disk with a higher density.
It is an object of the invention to provide rapid, reliable one-dimensional, two-dimensional, and three-dimensional tomographic complex amplitude imaging.
It is an object of the invention to provide an improved tomographic complex amplitude imaging technique that avoids the shortcomings of the above described prior art.
It is another object of the invention to provide a tomographic complex amplitude imaging technique that conveniently reduces or eliminates the statistical error effects of light from out-of-focus image points.
It is another object of the invention to provide an improved technique for tomographic complex amplitude imaging wherein systematic error effects of out-of-focus light images are greatly reduced or eliminated.
It is another object of the invention to provide a tomographic complex amplitude imaging technique that allows substantially simultaneous imaging of an object at multiple image points.
It is another object of the invention to provide a convenient technique for tomographic complex amplitude imaging in one, two, and three dimensions with the means to obtain a signal-to-noise ratio for the images that is achievable with an interferometric system.
It is another object of the invention to provide a tomographic complex amplitude imaging system and technique which avoids the computation difficulties of solving nonlinear differential equations.
It is another object of the invention to provide a convenient technique for tomographic complex amplitude imaging of a line section or two-dimensional section in an object despite movement thereof.
The embodiments and variants thereof described hereinafter fall into five groups of embodiments.
Certain ones of the embodiments and variants thereof of the first group of embodiments generate one-dimensional images that are substantially orthogonal to the one-dimensional images generated by corresponding ones of embodiments and variants thereof of the second group of embodiments, information in the one-dimensional images being acquired simultaneously with background reduction and compensation. Certain other ones of the embodiments of the first group of embodiments generate two-dimensional images that are substantially orthogonal to the two-dimensional images generated by corresponding ones of the embodiments and variants thereof of the second group of embodiments, information in the two-dimensional images being acquired simultaneously with background reduction and compensation.
Certain ones of the embodiments and variants thereof of the third group of embodiments generate one-dimensional images that are substantially orthogonal to the one-dimensional images generated by corresponding ones of embodiments and variants thereof of the fourth group of embodiments, information in the one-dimensional images being acquired simultaneously without background reduction and compensation. Certain other ones of the embodiments and variants thereof of the third group of embodiments generate two-dimensional images that are substantially orthogonal to the two-dimensional images generated by corresponding ones of the embodiments and variants thereof of the fourth group of embodiments, information in the two-dimensional images being acquired simultaneously without background reduction and compensation.
The embodiments and variants thereof of the fifth group of embodiments generate multi-dimensional images as a sequence of single point images, the single points images being acquired with background reduction and compensation.
Briefly described, and in accordance with one embodiment thereof, I provide a method and apparatus from the first group of embodiments for discriminating the complex amplitude of an in-focus image from the complex amplitude of an out-of-focus image by focusing optical radiation from a broadband spatially incoherent point source onto a source pinhole. Rays emanating from the source pinhole are collimated and directed to a first phase shifter. The phase of a first portion of the collimated rays is shifted by the phase shifter to produce a first quantity of phase-shifted rays, and the phase of a second portion of the collimated rays is shifted by the phase shifter to produce a second quantity of phase-shifted rays. The first and second quantities of phase-shifted rays are focused to a first spot.
Rays of the first quantity of phase-shifted rays emanating from the first spot are collimated and directed to a beam splitter. A first portion of the collimated rays passes through the beam splitter to form a first quantity of a probe beam and a second portion of the collimated rays is reflected by the beam splitter to form a first quantity of a reference beam. Rays of the second quantity of phase-shifted rays emanating from the first spot are collimated and directed to the beam splitter. A first portion of the collimated rays passes through the beam splitter to form a second quantity of the probe beam and a second portion of the collimated rays is reflected by the beam splitter to form a second quantity of the reference beam.
The rays of the first and second quantities of the probe beam are directed to a second phase-shifter. The rays of the first quantity of the probe beam are phase shifted to form a third quantity of the probe beam and rays of the second quantity of the probe beam are phase shifted to form a fourth quantity of the probe beam, the net phase shifts produced by the first and second phase shifters for the third and fourth quantities of the probe beam being the same. The third and fourth quantities of the probe beam are focused by a first probe lens to form a line image in an object material to thereby illuminate the object material. The line image is aligned proximally along the optical axis of the first probe lens and the length of the line image along the optical axis is determined by a combination of factors such as the depth of focus and chromatic aberration of the first probe lens which can be adjusted and the optical bandwidth of the source.
Rays of the first and second quantities of the reference beam are directed to a third phase-shifter. Rays of the first quantity of the reference beam are phase shifted to form a third quantity of the reference beam and rays of the second quantity of the reference beam are phase shifted to form a fourth quantity of the reference beam, the net phase shifts produced by the first and third phase shifters for the third and fourth quantities of the reference beam being the same. The third and fourth quantities of the reference beam are focused by a reference lens onto a spot on a reference mirror.
Reflected and/or scattered rays of the third and fourth quantities of the probe beam emanating from the illuminated object in the direction of the probe lens form a scattered probe beam and are collimated and directed by the probe lens to the second phase shifter. The phase of a first portion of the collimated rays is shifted to produce a first scattered probe beam quantity of phase-shifted rays, and the phase of a second portion of the collimated rays is shifted to produce a second scattered probe beam quantity of phase-shifted rays. Rays of the first and second scattered probe beam quantities are directed to the beam splitter. A portion of the first and a portion of the second scattered probe beam quantities are reflected by the beam splitter to form third and fourth quantities of the scattered probe beam, respectively. The collimated rays of the third and fourth quantities of the scattered probe beam are focused by a spatial filter lens onto a spatial filter pinhole.
Reflected rays emanating from the spot on the reference mirror in the direction of the reference lens form a reflected reference beam and are collimated and directed by the reference lens to the third phase shifter. The phase of a first portion of the collimated rays is shifted to produce a first reflected reference beam quantity of phase-shifted rays and the phase of a second portion of the collimated rays is shifted to produce a second reflected reference beam quantity of phase-shifted rays. Rays of the first and second reflected reference beam quantities are directed to the beam splitter. A portion of the first and second reflected reference beam quantities are transmitted by the beam splitter to form third and fourth quantities of the reflected reference beam, respectively. Collimated rays of the third and fourth quantities of the reflected reference beam are focused by the spatial filter lens onto the spatial filter pinhole.
A portion of the third and a portion of the fourth quantities of the scattered probe beam pass through the spatial filter pinhole to form spatially-filtered third and fourth quantities of scattered probe beam, respectively. The spatially-filtered third and fourth quantities of scattered probe beam are collimated and directed by a dispersive element lens to a dispersive element, preferably a reflecting diffraction grating.
A portion of the third and a portion of the fourth quantities of the reflected reference beam pass through the spatial filter pinhole to form spatially-filtered third and fourth quantities of reflected reference beam, respectively. The spatially-filtered third and fourth quantities of reflected reference beam are collimated and directed by the dispersive element lens to the dispersive element.
A portion of each of the spatially-filtered third and fourth quantities of scattered probe beam emanating from the dispersive element passes through a detector lens to form wavenumber-filtered, spatially-filtered third and fourth quantities of scattered probe beam, respectively. The wavenumber-filtered, spatially-filtered third and fourth quantities of scattered probe beam are focused by the detector lens to form a line image on a plane containing a linear array of detector pinholes. A portion of each of the spatially-filtered third and fourth quantities of reflected reference beam emanating from the dispersive element passes through the detector lens to form wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam, respectively. The wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam are focused by the detector lens to form a line image of wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam on the plane containing the linear array of pinholes.
Intensities of portions of superimposed wavenumber-filtered, spatially-filtered third and fourth quantities of scattered probe beam and the wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam transmitted by the detector pinholes are measured by a multi-pixel detector comprised of a linear array of pixels as a first array of measured intensity values. The phases of the wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam are shifted by xcfx80 radians by a fourth phase shifter to form a first phase-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam. Intensities of portions of superimposed wavenumber-filtered, spatially-filtered third and fourth quantities of scattered probe beam and the first phase-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam transmitted by the detector pinholes are measured by the multi-pixel detector as a second array of measured intensity values.
The phases of the wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam are shifted by an additional xe2x88x92xcfx80/2 radians by the fourth phase shifter to form a second phased-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam, respectively. Intensities of portions of superimposed wavenumber-filtered, spatially-filtered third and fourth quantities of scattered probe beam and the second phase-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam transmitted by the detector pinholes are measured by the multi-pixel detector as a third array of measured intensity values.
The phases of the wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam are shifted by an additional xcfx80 radians by the fourth phase shifter to form a third phase-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam, respectively. Intensities of portions of superimposed wavenumber-filtered, spatially-filtered third and fourth quantities of scattered probe beam and the third phase-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam transmitted by the detector pinholes are measured by the multi-pixel detector as a fourth array of measured intensity values.
In a next step, the first, second, third, and fourth arrays of measured intensity values are sent to a computer for processing. Elements of the second array of measured intensity values are subtracted from the corresponding elements of the first array of measured intensity values by the computer to yield a measurement of a first array of component values of a complex amplitude of the scattered probe beam that is in focus at the plane of the detector pinholes with the effects of light from out-of-focus images substantially canceled out. Elements of the fourth array of measured intensity values are subtracted from the corresponding elements of the third array of measured intensity values by the computer to yield a measurement of a second array of component values of the complex amplitude of the scattered probe beam that is in focus at the plane of the detector pinholes with the effects of light from out-of-focus images substantially canceled out.
The first and second arrays of component values of the amplitude of the scattered probe beam are values of orthogonal components and as such, give within a complex constant an accurate measurement of the complex amplitude of the scattered probe beam that is in-focus in the plane of the detector pinholes with the effects of light from out-of-focus images substantially canceled out. Using the computer and computer algorithms known to those skilled in the art, an accurate one-dimensional representation of a line section of the object material is obtained with no scanning of the object material required. The direction of the line section is in the direction of the optical axis of the probe lens. The line section may cut through one or more surfaces of the object material or lie in a surface of the object material. Using the computer and computer algorithms known to those skilled in the art, accurate two-dimensional and three-dimensional representations of the object material are obtained from two-dimensional and three-dimensional arrays, respectively, of the first, second, third, and fourth arrays of measured intensity values acquired through scanning of the object material in one and two dimensions, respectively. The two-dimensional and three-dimensional representations of the object material may include one or more surfaces of the object material. The scanning of the object material is achieved by systematically moving the object material in one and two dimensions, respectively, with a translator which is controlled by the computer. The computer algorithms may include computer deconvolutions and integral equation inversion techniques which are known to those skilled in the art should correction for out-of-focus images be desired beyond the compensation achieved in the first and second arrays of component values of the amplitude of the scattered probe beam by the apparatus of the present invention.
In accordance with a second embodiment thereof, I provide a method and apparatus for discriminating the complex amplitude of an in-focus image from the complex amplitude of an out-of-focus image by imaging optical radiation from a broadband, spatially extended, spatially incoherent line source onto a linear array of source pinholes comprising the apparatus and electronic processing means of the previously described embodiment wherein the source pinhole of the first embodiment has been replaced by the linear array of source pinholes, the spatial filter pinhole of the first embodiment has been replaced by a linear array of spatial filter pinholes, and the linear array of detector pinholes and the multi-pixel detector of the first embodiment have been replaced by a two-dimensional array of detector pinholes and a multi-pixel detector comprised of a two-dimensional array of pixels, respectively. The directions of the linear array of source pinholes and the linear array of spatial filter pinholes are perpendicular to the plane defined by the dispersive element. The two-dimensional arrays of detector pinholes and detector pixels are orientated with the image of the linear array of source pinholes in the in-focus plane at the multi-pixel detector.
Elements of measured arrays of first and second component values of amplitude of wavenumber-filtered, spatially-filtered scattered probe beam are values of orthogonal components and as such, give within a complex constant an accurate measurement of the complex amplitude of the scattered probe beam that is in-focus at the plane of the two-dimensional linear array of detector pinholes with the effects of light from out-of-focus images substantially canceled out. Using computer algorithms known to those skilled in the art, an accurate two-dimensional representation of a two-dimensional section of the object material is obtained with substantially no scanning required. The two-dimensional section is selected by the respective orientations of the linear array of source pinholes and of the optical axis of the probe lens. The two-dimensional section may cut through one or more surfaces of the object material or lie in a surface of the object material. Using computer algorithms known to those skilled in the art, accurate three-dimensional representations of the object are obtained from three-dimensional arrays of the first, second, third, and fourth intensity values acquired through scanning of the object in substantially one dimension. The three-dimensional representation of the object material may include representations of one or more surfaces of the object material. The computer algorithms may include computer deconvolutions and integral equation inversion techniques which are known to those skilled in the art should correction for out-of-focus images be desired beyond the compensation achieved in the first and second arrays of component values of the amplitude of the scattered probe beam by the apparatus of the present invention.
In accordance with a variant of the second embodiment thereof, I provide a method and apparatus for discriminating an in-focus image from an out-of-focus image by imaging optical radiation from a broadband spatially-extended, spatially-incoherent line source onto a source slit comprising the apparatus and electronic processing means of the previously described second embodiment where the linear array of source pinholes of the second embodiment has been replaced by the source slit and the linear array of spatial filter pinholes of the second embodiment has been replaced by a spatial filter slit. The directions of the source slit and the spatial filter slit are perpendicular to the plane defined by the dispersive element.
Elements of measured arrays of first and second component values of the amplitude of the wavenumber-filtered, spatially-filtered scattered probe beam are values of orthogonal components and as such, give within a complex constant an accurate measurement of the complex amplitude of the wavenumber-filtered, spatially-filtered scattered probe beam that is in-focus in the plane of the two-dimensional array of detector pinholes with the effects of light from out-of-focus images substantially canceled out. Using computer algorithms known to those skilled in the art, an accurate two-dimensional representation of a two-dimensional section of the object material is obtained with no scanning required. The two-dimensional section is selected by the respective orientations of the source slit and of the optical axis of the probe lens. Using the computer and computer algorithms known to those skilled in the art, accurate three-dimensional representations of the object material are obtained from three-dimensional arrays of the first, second, third, and fourth intensity values acquired through scanning of the object material in one-dimension. The scanning of the object material is achieved by systematically moving the object material in one dimension with a translator controlled by the computer. The computer algorithms may include computer deconvolutions and integral equation inversion techniques which are known to those skilled in the art should correction for out-of-focus images be desired beyond the compensation achieved by the apparatus of the present invention.
Alternative embodiments to the first and second preferred embodiments of the invention include the ability to improve and/or optimize the signal-to-noise ratio using additional optical means and substantially the same electronic processing means as are employed in the primary apparatus of the first and second preferred embodiments of the invention. The additional optical means comprises modified paths for the reference and probe beams whereby the amplitude of wavenumber-filtered, spatially-filtered reflected reference beam focused on a selected detector pinhole for either the first embodiment or the second embodiment can be adjusted relative to the amplitude of the wavenumber-filtered, spatially-filtered scattered probe beam imaged on the selected detector pinhole of either the first embodiment or the second embodiment, respectively.
In accordance with a third embodiment thereof, I provide a method and apparatus for discriminating the complex amplitude of an in-focus image from the complex amplitude of an out-of-focus image with means to adjust or improve and/or optimize the signal-to-noise ratio comprising the apparatus of the previously described first embodiment and an optical means to adjust the amplitude of a wavenumber-filtered, spatially-filtered reflected reference beam focused on a selected detector pinhole relative to the amplitude of a wavenumber-filtered, spatially-filtered scattered probe beam imaged on the selected detector pinhole. Rays from a broadband spatially incoherent point source are focused onto a source pinhole. Rays emanating from the source pinhole are collimated and directed to a first phase shifter. The phase of a first portion of the collimated rays is shifted to produce a first quantity of phase-shifted rays, and the phase of a second quantity of the collimated rays is shifted to produce a second quantity of phase-shifted rays.
The first and second quantities of phase-shifted rays impinge on a first beam splitter. A first portion of the first quantity of phase-shifted rays passes through the first beam splitter to form a first quantity of a probe beam and a second portion of the first quantity of phase shifted rays is reflected by the first beam splitter to form a first quantity of the reference beam. A first portion of the second quantity of phase-shifted rays passes through the first beam splitter to form a second quantity of the probe beam and a second portion of the second quantity of phase-shifted rays is reflected by the first beam splitter to form a second quantity of the reference beam. The first and second quantities of the probe beam are focused to a first probe beam spot. The first and second quantities of the reference beam are focused to a first reference beam spot.
Rays of the first quantity of the probe beam emanating from the first probe beam spot are collimated and directed to a second beam splitter. A portion of the collimated rays passes through the second beam splitter to form a third quantity of the probe beam. Rays of the second quantity of probe beam emanating from the first probe beam spot are collimated and directed to the second beam splitter. A portion of the collimated rays passes through the second beam splitter to form a fourth quantity of the probe beam. The rays of the third and fourth quantities of the probe beam are directed to a second phase shifter. The rays of the third quantity of the probe beam pass through the second phase shifter and are phase shifted to form a fifth quantity of the probe beam. The rays of the fourth quantity of the probe beam pass through the second phase shifter and are phase shifted to form a sixth quantity of the probe beam, the net phase shifts produced by the first and second phase shifters for the fifth and sixth quantities of the probe beam being the same.
Rays of the first quantity of the reference beam emanating from the first reference beam spot are collimated, directed to a third phase shifter, and emerge as a third quantity of the reference beam. Rays of the second quantity of the reference beam emanating from the first reference beam spot are collimated, directed to the third phase shifter, and emerge as a fourth quantity of the reference beam, the net phase shifts produced by the first and third phase shifters for the third and fourth quantities of the reference beam being the same. A portion of the third quantity of the reference beam is reflected by a third beam splitter to form a fifth quantity of the reference beam. A portion of the fourth quantity of the reference beam is reflected by the third beam splitter to form a sixth quantity of the reference beam. The collimated fifth and sixth quantities of the reference beam are focused by a reference lens onto a second reference beam spot on a reference mirror.
The collimated fifth and sixth quantities of the probe beam are focused by a probe lens to form a line image in an object material to thereby illuminate the object material. The line image is aligned proximally along the optical axis of the probe lens and the length of the line image along the optical axis is determined by a combination of factors such as the depth of focus and chromatic aberration of the probe lens and the optical bandwidth of the source.
Reflected and/or scattered rays of the fifth and sixth quantities of the probe beam emanating from the illuminated object in the direction of the probe lens form a scattered probe beam. The scattered probe beam is collimated by the probe lens and directed to the second phase shifter. The phase of a first portion of the collimated rays is shifted to produce a first scattered probe beam quantity of phase-shifted rays, and the phase of a second portion of the collimated rays is shifted to produce a second scattered probe beam quantity of phase-shifted rays. Rays of the first and second scattered probe beam quantities are directed to the second beam splitter. A portion of the first and second scattered probe beam quantities are reflected by the second beam splitter to form third and fourth quantities of the scattered probe beam, respectively. Collimated rays of the third and fourth quantities of the scattered probe beam are focused by a spatial filter lens onto a spatial filter pinhole.
Reflected rays emanating from the second reference beam spot on the reference mirror in the direction of the reference lens form a reflected reference beam and are collimated and directed by the reference lens to the third beam splitter. A portion of the reflected reference beam is transmitted by the third beam splitter and impinges on a fourth phase shifter. The phase of a first portion of the transmitted beam is shifted to produce a first reflected reference beam quantity of phase-shifted rays and the phase of a second portion of the transmitted beam is shifted to produce a second reflected reference beam quantity of phase-shifted rays. Rays of the first and second reflected reference beam quantities are directed to the second beam splitter. A portion of the first and second reflected reference beam quantities are transmitted by the second beam splitter to form third and fourth quantities of the reflected reference beam, respectively. Collimated rays of the third and fourth quantities of the reflected reference beam are focused by the spatial filter lens onto the spatial filter pinhole.
A portion of each of the third and fourth quantities of the scattered probe beam passes through the spatial filter pinhole to form a spatially-filtered third and fourth quantities of scattered probe beam, respectively. The spatially-filtered third and fourth quantities of scattered probe beam are collimated and directed by a dispersion element lens to a dispersive element, preferably a reflecting diffraction grating.
A portion of each of the third and fourth quantities of the reflected reference beam passes through the spatial filter pinhole to form a spatially-filtered third and fourth quantities of reflected reference beam, respectively. The spatially-filtered third and fourth quantities of reflected reference beam are collimated and directed by the dispersion element lens to the dispersive element.
A portion of each of the spatially-filtered third and fourth quantities of scattered probe beam emanating from the dispersive element passes through a detector lens to form wavenumber-filtered, spatially-filtered third and fourth quantities of scattered probe beam, respectively. The wavenumber-filtered, spatially-filtered third and fourth quantities of scattered probe beam are focused by the detector lens to form a line image on a plane containing a linear array of detector pinholes. A portion of each of the spatially-filtered third and fourth quantities of reflected reference beam emanating from the dispersive element passes through the detector lens to form wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam, respectively. The wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam are focused by the detector lens to form a line image on the plane containing the linear array of detector pinholes.
Intensities of portions of superimposed wavenumber-filtered, spatially-filtered third and fourth quantities of scattered probe beam and the wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam transmitted by the detector pinholes are measured by a multi-pixel detector comprised of a linear array of pixels as a first array of measured intensity values. The phases of the wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam are shifted by xcfx80 radians by a fifth phase shifter to form a first phase-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam. Intensities of portions of superimposed wavenumber-filtered, spatially-filtered third and fourth quantities of scattered probe beam and first phase-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reference beam transmitted by the detector pinholes are measured by the multi-pixel detector as a second array of measured intensity values.
The phases of the wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam are shifted by an additional xe2x88x92xcfx80/2 radians by the fifth phase shifter to form a second phase-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam, respectively. Intensities of portions of superimposed wavenumber-filtered, spatially-filtered third and fourth quantities of scattered probe beam and of the second phase-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam transmitted by the detector pinholes are measured by the multi-pixel detector as a third array of measured intensity values.
The phases of the wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam are shifted by an additional xcfx80 radians by the fifth phase shifter to form a third phase-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam, respectively. Intensities of portions of superimposed wavenumber-filtered, spatially-filtered third and fourth quantities scattered probe beam and third phase-shifted, wavenumber-filtered, spatially-filtered third and fourth quantities of reflected reference beam transmitted by the detector pinholes are measured by the multi-pixel detector as a fourth array of measured intensity values.
In a next step, the first, second, third, and fourth arrays of measured intensity values are sent to a computer for processing. Elements of the second array of measured intensity values are subtracted from the corresponding elements of the first array of measured intensity values by the computer to yield a measurement of a first array of component values of a complex amplitude of the scattered probe beam that is in focus at the plane of the detector pinholes with the effects of light from out-of-focus images substantially canceled out. Elements of the fourth array of measured intensity values are subtracted from the corresponding elements of the third array of measured intensity values by the computer to yield a measurement of a second array of component values of the complex amplitude of the scattered probe beam that is in focus at the plane of the detector pinholes with the effects of light from out-of-focus images substantially canceled out.
Elements of first and second arrays of component values of the amplitude of wavenumber-filtered, spatially-filtered scattered probe beam are values of orthogonal components and as such, give within a complex constant an accurate measurement of the complex amplitude of the scattered probe beam that is in-focus in the plane of the detector pinholes with the effects of light from out-of-focus images substantially canceled out. Using the computer and computer algorithms known to those skilled in the art, an accurate one-dimensional representation of a line section of the object material is obtained with no scanning of the object material required. The direction of the line section is in the direction of the optical axis of the probe lens. Using the computer and computer algorithms known to those skilled in the art, accurate two-dimensional and three-dimensional representations of the object material are obtained from two-dimensional and three-dimensional arrays, respectively, of the first, second, third, and fourth arrays of measured intensity values acquired through scanning of the object material in one and two dimensions, respectively. The scanning of the object material is achieved by systematically moving the object material in one and two dimensions, respectively, with a translator which is controlled by the computer. The computer algorithms may include computer deconvolutions and integral equation inversion techniques which are known to those skilled in the art should correction for out-of-focus images be desired beyond the compensation achieved in the first and second arrays of component values of the amplitude of the scattered probe beam by the apparatus of the present invention.
The signal-to-noise ratio can be adjusted or improved and/or optimized in the third embodiment with respect to measuring the desired complex amplitudes. The optimization is accomplished by adjusting the ratio of the amplitude of the wavenumber-filtered, spatially-filtered third and fourth quantities of the scattered probe beam focused on a selected detector pinhole and of the amplitude of the wavenumber-filtered, spatially-filtered third and fourth quantities of the reflected reference beam focused on the selected detector pinhole by altering the reflection-transmission properties of the first, second, and third beam splitters.
In accordance with a fourth embodiment thereof, I provide a method and apparatus for discriminating the complex amplitude of an in-focus image from the complex amplitude of an out-of-focus image with means to adjust or improve and/or optimize the signal-to-noise ratio by imaging optical radiation from a broadband, spatially extended, spatially incoherent line source onto a linear array of source pinholes comprising the apparatus and electronic processing means of the previously described third embodiment wherein the source pinhole of the third embodiment has been replaced by the linear array of source pinholes, the spatial filter pinhole of the third embodiment has been replaced by a linear array of spatial filter pinholes, and the linear array of detector pinholes and the multi-pixel detector of the third embodiment have been replaced by a two-dimensional array of detector pinholes and a multi-pixel detector comprised of a two-dimensional array of pixels, respectively. The directions of the linear array of source pinholes and of the linear array of spatial filter pinholes are perpendicular to the plane defined by the dispersive element. The two-dimensional linear arrays of detector pinholes and detector pixels are orientated with the image of the linear array of source pinholes in the in-focus plane at the multi-pixel detector.
Elements of measured arrays of first and second component values of amplitude of wavenumber-filtered, spatially-filtered quantities of scattered probe beam are values of orthogonal components and as such, give within a complex constant an accurate measurement of the complex amplitude of the scattered probe beam that is in-focus at the plane of the two-dimensional linear array of detector pinholes with the effects of light from out-of-focus images substantially canceled out. Using the computer and computer algorithms known to those skilled in the art, an accurate two-dimensional representation of a two-dimensional section of the object material is obtained with substantially no scanning required. The two-dimensional section is selected by orientations of the linear array of source pinholes and of the optical axis of the probe lens. Using the computer and computer algorithms known to those skilled in the art, accurate three-dimensional representations of the object are obtained from three-dimensional arrays of the first, second, third, and fourth intensity values acquired through scanning of the object material in substantially one dimension. The computer algorithms may include computer deconvolutions and integral equation inversion techniques which are known to those skilled in the art should correction for out-of-focus images be desired beyond the compensation achieved in the first and second arrays of component values of the amplitude of the scattered probe beam by the apparatus of the present invention.
The signal-to-noise ratio obtained in the fourth embodiment can be adjusted or improved and/or optimized with respect to measuring the desired complex amplitudes. The adjustment or improvement and/or optimization is accomplished by adjusting the ratio of the amplitude of the wavenumber-filtered, spatially-filtered third and fourth quantities of the scattered probe beam focused on a selected detector pinhole and of the amplitude of the wavenumber-filtered, spatially-filtered third and fourth quantities of the reflected reference beam focused on the selected detector pinhole by altering the reflection-transmission properties of the first, second, and third beam splitters.
In accordance with a variant of the fourth embodiment thereof, I provide a method and apparatus for discriminating an in-focus image from an out-of-focus image by imaging optical radiation from a broadband spatially-extended, spatially-incoherent line source onto a source slit comprising the apparatus and electronic processing means of the previously described fourth embodiment where the linear array of source pinholes of the fourth embodiment has been replaced by the source slit and the linear array of spatial filter pinholes of the fourth embodiment has been replaced by a spatial filter slit. The directions of the source slit and the spatial filter slit are perpendicular to the plane defined by the dispersive element.
Elements of measured arrays of first and second component values of the amplitude of the wavenumber-filtered, spatially-filtered scattered probe beam are values of orthogonal components and as such, give within a complex constant an accurate measurement of the complex amplitude of the wavenumber-filtered, spatially-filtered scattered probe beam that is in-focus in the plane of the two-dimensional array of detector pinholes with the effects of light from out-of-focus images substantially canceled out. Using computer algorithms known to those skilled in the art, an accurate two-dimensional representation of a two-dimensional section of the object material is obtained with no scanning required. The two-dimensional section is selected by respective orientations of the source slit and of the optical axis of the probe lens. Using the computer and computer algorithms known to those skilled in the art, accurate three-dimensional representations of the object material are obtained from three-dimensional arrays of the first, second, third, and fourth intensity values acquired through scanning of the object material in one-dimension. The scanning of the object material is achieved by systematically moving the object material in one dimension with a translator controlled by the computer. The computer algorithms may include computer deconvolutions and integral equation inversion techniques which are known to those skilled in the art should correction for out-of-focus images be desired beyond the compensation achieved by the apparatus of the present invention.
In accordance with the above first, second, third, and fourth embodiments and their variants, the apparatus of the present invention employs a probe lens which may have an extended range in focus as a function of wavelength while maintaining a high lateral spatial resolution for each frequency component. The range in focus may be extended beyond the region defined by the numerical aperture of the probe lens for a single wavelength by employing a lens whose focal length is designed to be dependent upon wavelength. The wavelength dependence may be designed into the lens by using techniques known to those skilled in the art. Such techniques include the design of lens multiplets comprised of refractive materials of differing dispersion. The lens design may also include zone plates. If zone plates are used, the probe lens unit is preferable designed so that most of an optical beam component at a given wavelength is in focus in one order of the zone plates. The zone plates may be generated by holographic techniques. To take advantage of the extended range in focus, the beam from the source must be comprised of properties to match the properties of the probe lens, i.e. have a wavelength bandwidth matched to the range in wavelength of the probe lens.
The first, second, third, and fourth embodiments and variants thereof comprise the first group of embodiments. The second group of embodiments comprise the fifth, sixth, seventh, and eighth embodiments and variants thereof. The fifth, sixth, seventh, and eighth embodiments and variants thereof correspond to certain modified configurations of the first, second, third, and fourth embodiments and variants thereof, respectively, wherein the first probe lens of the first group of embodiments having an axial or longitudinal chromatic aberration is replaced with a probe lens having a lateral chromatic aberration. The probe lens with lateral chromatic aberration generates for the embodiments and variants thereof of the second group of embodiments a line image in the object material that is aligned proximally perpendicular to the optical axis of the respective probe lens and image points of the line image are acquired substantially simultaneously.
The length of the line image perpendicular to the optical axis of the respective probe lens is determined by a combination of factors such as the focal length of the respective probe lens and the magnitude of the lateral chromatic aberration of the respective probe lens, both of which can be adjusted, and the optical bandwidth of the source.
The third group of embodiments comprise the ninth, tenth, eleventh, and twelfth embodiments and variants thereof. The ninth, tenth, eleventh, and twelfth embodiments and variants thereof correspond to certain other modified configurations of the first, second, third, and fourth embodiments and variants thereof, respectively, wherein the multi-element phase shifters have not been incorporated. The omission of the multi-element phase shifters reduces the degree of reduction and compensation of background from out-of-focus images for the third group of embodiments. The probe lens for the third group of embodiments, the probe lens having axial chromatic aberration, generates a line image in an object material. The line image is aligned proximally along the optical axis of the probe lens having axial chromatic aberration and image points of the line image are acquired substantially simultaneously.
The fourth group of embodiments comprise the embodiments 13, 14, 15, and 16 and variants thereof. The embodiments 13, 14, 15, and 16 and variants thereof correspond to certain modified configurations of the fifth, sixth, seventh, and eighth embodiments and variants thereof, respectively, wherein the multi-element phase shifters have not been incorporated. The omission of the multi-element phase shifters reduces the degree of reduction and compensation of background from out-of-focus images for the fourth group of embodiments. The probe lens for the fourth group of embodiments, the probe lens having lateral chromatic aberration, generates a line image in an object material. The line image is aligned proximally orthogonal to the optical axis of the probe lens having lateral chromatic aberration and image points of the line image are acquired substantially simultaneously.
The fifth group of embodiments comprise embodiments 17, 18, 19, and 20 and variants thereof. The embodiments 17, 18, 19, and 20 and variants thereof correspond to a second set of certain other modified configurations of the first, second, third, and fourth embodiments and variants thereof, respectively, wherein the probe lens having axial chromatic aberration is replaced with a probe lens substantially free of axial chromatic aberration. The image generated in an object material by embodiments of the fifth group is nominally a point image. The degree of reduction and compensation for background from out-of-focus images for embodiments and variants thereof of the fifth group of embodiments is the same as the degree of reduction and compensation for background from out-of-focus images for corresponding embodiments and variants thereof of the first group of embodiments. The image points for the embodiments and variants thereof of the fifth group of embodiments are acquired sequentially in time.
In accordance with the embodiments and variants thereof of the first four groups of embodiments, the signal-to-noise ratio may be also adjusted and/or optimized for multiple optical frequency components of the source. This is achieved by placing a wavelength filter in the paths of the reference and/or reflected reference beams, preferably, and/or in the paths of the probe and/or scattered probe beams and constructing the transmission of the wavelength filter to have a specific wavelength dependence to adjust and/or optimize the ratio of the wavenumber-filtered, spatially-filtered reflected reference beam and the wavenumber-filtered, spatially-filtered scattered probe beam transmitted through respective detector pinholes for different wavelengths. This feature can be particularly valuable when there is a strong attenuation of the probe and scattered probe beams in passing through the object material.
For each of the embodiments and variants thereof of the five groups of embodiments, there is a corresponding embodiment or variant for writing information to an object material comprising a recording medium. Each embodiment and variant thereof for writing information comprises method and apparatus of a corresponding embodiment or variant except for the following changes in configuration: the source and reference mirror subsystems are interchanged and the detector and detector pinholes are replaced by a mirror wherein the mirror directs the light from the source impinging on the mirror substantially back on itself with a temporally and spatially dependent degree of reflectivity and a temporally and spatially dependent phase shift introduced by the mirror arranged in conjunction with a phase-shifting procedure to produce the desired images in the object material. The phase-shifting procedure performs a function analogous to the procedure of introducing a sequence of phase shifts in the wavenumber-filtered, spatially-filtered reflected reference beam to obtain first, second, third, and fourth measured intensity values for the embodiments and variants thereof of the five groups of embodiments.
For certain ones of the writing embodiments and variants thereof described herein, a single bit binary format is used to store information at a given location in the object material. In certain other ones of the embodiments and variants thereof described herein, a higher density of information storage than that achievable in the certain ones of the embodiments and variants thereof is obtained by recording in a base N format for amplitude or (base N)xc3x97(base M) format for amplitude and phase information at each data storage site in an amplitude or amplitude and phase recording medium.
It should be appreciated by those skilled in the art that the procedure of introducing a sequence of phase shifts in the wavenumber-filtered, spatially-filtered reflected reference beam to obtain the first, second, third, and fourth measured intensity values for the cited embodiments and variants may also be implemented with phase-sensitive detection and heterodyne detection techniques without departing from the scope and spirit of the present invention. For example, the phase shifting procedure comprised of four discrete phase shift values of 0, xcfx80, xe2x88x92xcfx80/2, and xcfx80 radians may be replaced by a sinusoidal phase variation of amplitude xcex2 at frequency xcfx89. The first and second component values of the complex amplitude of wavenumber-filtered, spatially filtered scattered probe beam are detected by phase-sensitive detection as the first and second harmonics of xcfx89, respectively. The amplitude xcex2 is chosen so that there is a high sensitivity for detection of both the first and second harmonics. In a second example, the frequency of the reference beam is shifted with respect to the frequency of the probe beam, for example by an acousto-optical modulator, and the first and second component values of the complex amplitude of wavenumber-filtered, spatially filtered scattered probe beam are acquired by heterodyne detection.
It should be appreciated by those skilled in the art that the embodiments and variants thereof for writing information to optical disks may write information at memory sites in single bit binary format. It will be further appreciated by those skilled in the art that the embodiments and variants thereof for writing information to optical disks may write information in the form of base N format for amplitude or (base N)xc3x97(base M) format for amplitude and phase at a memory site or as transforms in (base N)xc3x97(base M) format of information to be stored, transforms such as Fourier transforms or Hilbert transforms.
It should be appreciated by those skilled in the art that information may be stored in a medium by the magneto-optical effect and that the information stored is retrieved by measuring changes in the polarization state of a probe beam scattered or transmitted by the object material.
It should be appreciated by those skilled in the art that the desired scanning of the object material in embodiments and variants thereof of the five groups of embodiments and the associated writing embodiments and variants thereof may also be achieved by scanning the image of the respective source pinhole, the linear array of source pinholes or the source slit in the object material with the object material remaining stationary.
It should be appreciated that the xe2x80x9cenabling technologyxe2x80x9d of the invention applies for any electromagnetic radiation, electron beams as used for example in electron microscopes, or even acoustic waves for which suitable collimating lenses, imaging lenses, phase shifters, and recording mediums can be provided. For applications wherein the amplitude of the beam is detected instead of the intensity, the function of producing the square of the amplitude must be done in the electronic processing following the detector.
It should also be appreciated that the length of the line image in the object material can be altered by changing for example the depth of focus and/or the axial chromatic aberration of the probe lens or the lateral chromatic aberration of the probe lens with the requisite corresponding changes in the optical bandwidth of the source.
The line source need not be spatially incoherent in the direction of the line source in the case of either the second or fourth preferred embodiments or their respective variants to achieve a reduced systematic error although the systematic error will generally be lower when a spatially incoherent line source is used.
An advantage of certain ones of the first and third groups of embodiments with respect to reading a multiple-layer, multiple-track optical disk is the substantially simultaneous imaging of a line section in the depth direction of the optical disk with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that obtained in a sequence of measurements with prior art single-pinhole confocal interference microscopy or holography. The simultaneous imaging of a line section in the depth direction of the optical disk can be used to greatly reduce sensitivity to motion of the optical disk in the depth direction generated by rotation of the optical disk, non-flatness of the optical disk, and/or vibrations of the optical disk. The simultaneous imaging of a line section in the depth direction of the optical disk can further be used to identify a reference surface in the optical disk with information acquired simultaneously from multiple layers, the reference layer serving registration purposes.
An advantage of certain ones of the first and third groups of embodiments with respect to providing a tomographic complex amplitude image of a wafer used in the fabrication of integrated circuits is the substantially simultaneous imaging of a line section in the depth direction of the wafer with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that obtained in a sequence of measurements with prior art single-pinhole confocal interference microscopy or holography. The simultaneous imaging of a line section in the depth direction of the wafer can be used to greatly reduce sensitivity to motion of the wafer in the depth direction generated by for example by translations, scanning, or vibrations of the wafer. The simultaneous imaging of a line section in the depth direction of the wafer can further be used to identify a surface of and/or in the wafer with information acquired simultaneously from multiple depths.
An advantage of certain ones of the first and third groups of embodiments with respect to providing a tomographic complex amplitude image of a biological specimen in vivo, an image which can be used for example in a non-invasive biopsy of the biological specimen, is the substantially simultaneous imaging of a line section in the depth direction of the biological specimen with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that obtained in a sequence of measurements with prior art single-pinhole confocal interference microscopy or holography. The simultaneous imaging of a line section in the depth direction of the biological specimen can be used to greatly reduce sensitivity to motion of the biological specimen in the depth direction generated by for example by translations, scanning, or vibrations of the biological specimen. The simultaneous imaging of a line section in the depth direction of the biological specimen can further be used to identify a surface of and/or in the biological specimen with information acquired simultaneously from multiple depths.
Another advantage of certain other ones of the first and third groups of embodiments with respect to reading a multiple-layer, multiple-track optical disk is the substantially simultaneous imaging of a two-dimensional section of the optical disk significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that obtained in a sequence of measurements with prior art single-pinhole and slit confocal interference microscopy or holography. One axis of the two-dimensional section of the optical disk is parallel to the depth direction of the optical disk and the orthogonal axis of the two-dimensional section of the optical disk may be either parallel to radial direction of the optical disk or parallel to a tangent to a track in the optical disk. The simultaneous imaging of a two-dimensional section of the optical disk can be used to greatly reduce sensitivity to motion of the optical disk in the depth and radial directions generated by rotation of the optical disk, non-flatness of the optical disk, and/or vibrations of the optical disk. The simultaneous imaging of a two-dimensional section in the optical disk can further be used to identify a reference surface, i.e. reference layer, and a reference track in or on the optical disk or used for track identification with information acquired simultaneously at multiple layers and multiple tracks, the reference layer and reference track serving registration purposes.
Another advantage of certain other ones of the first and third groups of embodiments with respect to providing a tomographic complex amplitude image of a wafer used in the fabrication of integrated circuits is the substantially simultaneous imaging of a two-dimensional section of the wafer with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that obtained in a sequence of measurements with prior art single-pinhole and slit confocal interference microscopy or holography. One axis of the two-dimensional section of the wafer is parallel to the depth direction of the wafer. The simultaneous imaging of a two-dimensional section of the wafer can be used to greatly reduce sensitivity to motion of the wafer in the depth and transverse directions generated by translation, scanning, and/or vibrations of the wafer. The simultaneous imaging of a two-dimensional section in the wafer can further be used to identify a surface or internal surface of the wafer with information acquired simultaneously at other locations, the surface and/or internal surface possibly serving registration purposes.
Another advantage of certain other ones of the first and third groups of embodiments with respect to providing a tomographic complex amplitude image of a biological specimen in vivo, an image which can be used for example in a non-invasive biopsy of the biological specimen, is the substantially simultaneous imaging of a two-dimensional section of the biological specimen with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that obtained in a sequence of measurements with prior art single-pinhole and slit confocal interference microscopy or holography. One axis of the two-dimensional section of the biological specimen is parallel to the depth direction of the wafer. The simultaneous imaging of a two-dimensional section of the wafer can be used to greatly reduce sensitivity to motion of the biological specimen in the depth and transverse directions generated by translation, scanning, and/or vibrations of the biological specimen. The simultaneous imaging of a two-dimensional section in the biological specimen can further be used to identify a surface or internal surface of the biological specimen with information acquired simultaneously at other locations, the surface and/or internal surface possibly serving registration purposes.
An advantage of certain ones of the second and fourth groups of embodiments with respect to reading a multiple-layer, multiple-track optical disk is the substantially simultaneous imaging of a line section tangent to a layer in or on the optical disk with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that obtained in a sequence of measurements with prior art single-pinhole confocal interference microscopy or holography. The simultaneous imaging of a line section tangent to a layer in or on the optical disk can be used to greatly reduce sensitivity to motion of the optical disk generated by rotation of the optical disk and/or vibrations of the optical disk. The simultaneous imaging of a two-dimensional section tangent to a layer in or on the optical disk can further be used to identify a reference track in the optical disk with information acquired simultaneously from multiple tracks, the reference track serving registration purposes.
An advantage of certain ones of the second and fourth groups of embodiments with respect to providing a tomographic complex amplitude image of a wafer used in the fabrication of integrated circuits is the substantially simultaneous imaging of a line section tangent to a surface of the wafer or on a surface in the wafer with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that obtained in a sequence of measurements with prior art single-pinhole confocal interference microscopy or holography. The simultaneous imaging of a line section tangent to a surface of the wafer or on a surface in the wafer can be used to greatly reduce sensitivity to motion of the wafer generated by translations, scanning, and/or vibrations of the wafer. The simultaneous imaging of a two-dimensional section tangent to a surface in or on the wafer can further be used to identify a reference location in or/on the wafer with information acquired simultaneously from locations, the reference location serving registration purposes.
An advantage of certain ones of the second and fourth groups of embodiments with respect to providing a tomographic complex amplitude image of a biological specimen in vivo, an image which can be used for example in a non-invasive biopsy of the biological specimen, is the substantially simultaneous imaging of a line section tangent to a surface in or on the specimen with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that obtained in a sequence of measurements with prior art single-pinhole confocal interference microscopy or holography. The simultaneous imaging of a line section tangent to a surface in or on the specimen can be used to greatly reduce sensitivity to motion of the specimen generated by translation, scanning, and/or vibrations of the specimen. The simultaneous imaging of a two-dimensional section tangent to a surface in or on the specimen can further be used to identify a reference location in the specimen with information acquired simultaneously from multiple locations, the reference location serving registration purposes.
Another advantage of certain other ones of the second and fourth groups of embodiments with respect to reading a multiple layer, multiple-track optical disk is the substantially simultaneous imaging of a two-dimensional section of the optical disk with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that obtained in a sequence of measurements with prior art single-pinhole and slit confocal interference microscopy or holography. One axis of the two-dimensional section of the optical disk may be parallel to the radial direction of the optical disk and the orthogonal axis of the two-dimensional section of the optical disk may be parallel to a tangent to a track in or on the optical disk. The simultaneous imaging of a two-dimensional section of the optical disk can be used to greatly reduce sensitivity to motion of the optical disk in the radial direction generated by rotation of the optical disk and/or vibrations of the optical disk. The simultaneous imaging of a two-dimensional section in or on the optical disk can further be used to identify a reference track for track identification and for read errors for a given track with information acquired simultaneously at multiple tracks and multiple positions on the multiple tracks, the reference track serving registration purposes.
An advantage of the fifth group of embodiments with respect to reading a multiple-layer, multiple-track optical disk is the generation of an one-dimensional, two-dimensional or three-dimensional image of a multiple-layer, multiple-track optical disk with a background from out-of-focus images significantly reduced compared to that obtained in a sequence of measurements with prior art single-pinhole confocal interference microscopy or holography.
An advantage of the fifth group of embodiments with respect to providing a tomographic complex amplitude image of a wafer used in the fabrication of integrated circuits is the generation of an one-dimensional, two-dimensional, or three-dimensional image of a wafer with a background from out-of-focus images significantly reduced compared to that obtained in a sequence of measurements with prior art single-pinhole confocal interference microscopy or holography.
An advantage of the fifth group of embodiments with respect to providing a tomographic complex amplitude image of a biological specimen in vivo, an image which can be used for example in a non-invasive biopsy of the biological specimen, is the generation of an one-dimensional, two-dimensional, or three-dimensional image of the specimen with a background from out-of-focus images significantly reduced compared to that obtained in a sequence of measurements with prior art single-pinhole confocal interference microscopy or holography.
An advantage of the first four groups of embodiments of the invention is the substantially simultaneous imaging of a line section with a background from out-of-focus images significantly reduced compared to or the same as that obtained in a sequence of measurements with prior art single-pinhole confocal interference microscopy. The substantially simultaneous imaging feature is made possible by the introduction of the technique called xe2x80x9coptical wavenumber domain reflectometryxe2x80x9d (OWDR). The reduction of the background is made possible by the adaptation of the basic principal of pinhole confocal microscopy to an interferometric measuring system. The substantially simultaneous imaging feature makes it possible to generate one-dimensional, two-dimensional, and three-dimensional images with greatly reduced sensitivity to motion of the object during the measurement process. The problem of motion can pose serious limitations in technologies currently employed in the case of in vivo measurements of biological systems. In PSI and SCLI where the technology disclosed herein is not incorporated, serious limitations are encountered due to motion caused by vibrations. The problem of untracked motion can also pose serious limitations in the reading and/or writing to a multiple-layer, multiple-track optical disk.
Another advantage of the invention is the substantially simultaneous imaging of a two-dimensional section with a background from out-of-focus images significantly reduced compared to that obtained in a sequence of measurements with prior art slit confocal interference microscopy. The substantially simultaneous imaging feature is made possible by the introduction of the OWDR technique. The reduction of the background is made possible by the adaptation of the basic principal of slit confocal microscopy to an interferometric measuring system. The substantially simultaneous imaging feature makes it possible to generate two-dimensional and three-dimensional images with greatly reduced sensitivity to motion of the object during the measurement process. As already noted, the problem of motion can pose serious limitations in technologies currently employed in the case of in vivo measurements of biological systems, in PSI and SCLI due to motion caused by vibrations, and in reading and/or writing to a multiple-layer, multiple-track optical disks due to untracked motion.
An advantage of certain ones of the embodiments and variants thereof for writing to a multiple-layer, multiple-track optical disk, embodiments and variants thereof corresponding to certain ones of the first and third groups of embodiments, is the substantially simultaneous imaging of a line section in the depth direction in the optical disk with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that generated in a sequence of images with prior art single-pinhole confocal interference microscopy or holographic imaging. The simultaneous imaging of a line section in the depth direction in the optical disk can be used to greatly reduce sensitivity to motion of the optical disk in the depth direction generated by rotation of the optical disk, non-flatness of the optical disk, and/or vibrations of the optical disk. The simultaneous imaging of a line section in the depth direction in the optical disk can further be used to generate a reference surface in the optical disk simultaneously with the writing of information at multiple layers, the reference layer serving registration purposes.
Another advantage of certain other ones of the embodiments and variants thereof for writing to a multiple-layer, multiple-track optical disk, embodiments and variants thereof corresponding to certain other ones of the first and third groups of embodiments, is the substantially simultaneous imaging of a two-dimensional section in the optical disk with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that generated in a sequence of images with prior art single-pinhole and slit confocal interference microscopy or holography. One axis of the two-dimensional section in the optical disk is substantially parallel to the depth direction of the optical disk and the orthogonal axis of the two-dimensional section in the optical disk may be either substantially parallel to a radial direction of the optical disk, substantially parallel to a tangent to a track in the optical disk, or any the directions in between. The simultaneous imaging of a two-dimensional section in the optical disk can be used to greatly reduce sensitivity to motion of the optical disk in the depth and orthogonal directions generated by rotation of the optical disk, non-flatness of the optical disk, and/or vibrations of the optical disk. The simultaneous imaging of a two-dimensional section in the optical disk can further be used to generate a reference surface, i.e. reference layer, and a reference track in or on the optical disk simultaneously with information being imaged at multiple layers and multiple tracks, the reference layer and reference track serving registration purposes.
An advantage of certain ones of the embodiments and variants thereof for writing to a multiple-layer, multiple-track optical disk, embodiments and variants thereof corresponding to certain ones of the second and fourth groups of embodiments is the substantially simultaneous imaging of a line section tangent to a layer in or on the optical disk with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that generated in a sequence of images with prior art single-pinhole confocal interference microscopy or holography. The simultaneous imaging of a line section tangent to a layer in or on the optical disk can be used to greatly reduce sensitivity to motion of the optical disk generated by rotation of the optical disk and/or vibrations of the optical disk.
Another advantage of certain other ones of the embodiments and variants thereof for writing to a multiple layer, multiple-track optical disk, embodiments and variants thereof corresponding to certain other ones of the second and fourth groups of embodiments, is the substantially simultaneous imaging of a two-dimensional section of the optical disk with significantly reduced statistical errors and with a background from out-of-focus images significantly reduced compared to or the same as that generated in a sequence of images with prior art single-pinhole and slit confocal interference microscopy or holography. One axis of the two-dimensional section of the optical disk may be substantially parallel to a radial direction on the optical disk and the orthogonal axis of the two-dimensional section on the optical disk may be substantially parallel to a tangent to a track in or on the optical disk. The simultaneous imaging of a two-dimensional section of the optical disk can be used to greatly reduce sensitivity to motion of the optical disk in the radial directions generated by rotation of the optical disk and/or vibrations of the optical disk. The simultaneous imaging of a two-dimensional section in or on the optical disk can further be used to generate a reference track for track identification simultaneously with writing information at multiple tracks and multiple positions on the multiple tracks, the reference track serving registration purposes.
An advantage of embodiments and variants thereof for writing to a multiple-layer, multiple-track optical disk, embodiments and variants thereof corresponding to the fifth group of embodiments, is the generation of an one-dimensional, two-dimensional, or three-dimensional image on a multiple-layer, multiple-track optical disk with a background from out-of-focus images significantly reduced compared to that generated in a sequence of images with prior art single-pinhole confocal interference microscopy or holography.
An advantage of the invention is that the complex scattering amplitude of the object is obtained instead of the magnitude of the scattering amplitude as in the case of PCI and OCT. This is particularly important with respect to the amount of computer analysis required to obtain a given type of one-dimensional, two-dimensional or three-dimensional images of the object material.
Another advantage is that the computer processing required to obtain the complex scattering amplitude in one-dimensional, two-dimensional, and three-dimensional imaging is greatly reduced compared to that required in prior art confocal systems currently employed.
Another advantage is that if it is necessary to correct for out-of-focus images which are already greatly reduced in the apparatus of the present invention, the computer processing required to achieve a given level of correction with the apparatus of the present invention is significantly reduced compared to the computer processing required in prior art scanning single-pinhole and scanning slit confocal and scanning single-pinhole and scanning slit confocal interference microscopy.
Another advantage is that for the single source pinhole, the contribution of background radiation to the statistical noise in the measured complex scattering amplitude over a given transverse distance in the object material for a given measurement interval of time can be reduced in the respective embodiments and variant of the present invention below that obtainable for the same interval of time in prior art scanning single-pinhole confocal interference microscopy by a factor which is substantially proportional to the square root of the number of independent measurement positions over the axial image distance where independent is with respect to the measured complex scattering amplitude. A similar advantage is also present with respect to slit confocal interference microscopy where the corresponding reduction factor is substantially proportional to the square root of the number of independent measurement positions over an imaged two-dimensional section of the object material.
Another advantage is that the contribution of background radiation to the statistical noise in the measured complex scattering amplitude over a given imaged axial distance for a given measurement interval of time can be reduced to that which derives principally from the size of the complex scattering amplitude itself, a particularly important advantage for the case where the amplitude of the background radiation is relatively large compared to the size of the complex scattering amplitude. This is not achievable in prior art scanning single-pinhole or slit confocal microscopy.
Another advantage is that for certain embodiments and variants thereof of the first four groups of embodiments, a scan substantially in only one dimension is required to produce a two-dimensional image and only a scan substantially in two dimensions is required to produce a three-dimensional image.
Another advantage is that for certain other embodiments and variants thereof of the first four groups of embodiments, a scan substantially in only one dimension is required to produce a three-dimensional image.
The apparatus of the instant invention can, in summary, be operated to (1) reduce systematic error, (2) reduce statistical error, (3) reduce dynamic range requirements for detector, processing electronics, and recording medium, (4) increase the density of data stored in optical disks, (5) reduce the computer processing required to generate either a one-dimensional, two-dimensional, or three-dimensional images, (6) reduce the computer processing required to correct for systematic error effects of out-of-focus images, and/or (7) can be operative when imaging through a turbid medium. Generally, one or more of these features can be implemented for operation in parallel.